Think you may be looking at the wrong switch @terryplumb. The top one in the 3rd url is marked ON OFF but that is only the manual one I use to top up during the day. If you look at the bottom of the picture, that is the one I'm not sure about as it has no ON OFF marking, just a little red light...
Sorry not sure what you mean? If you look at the third URL you can see the bottom switch doesn't have ON OFF printed on it, only the top red switch does. The second URL shows the top switch in its ON position. Here's a picture of the fusebox
https://ibb.co/7j6CmXr
@terryplumb
Water heater...
It's an electric boiler with two switches. The red switch turns it on manually but uses expensive day rate electricity. The bottom switch is supposed to let it come on overnight but I'm not sure how to tell if it on or not? There's no text saying on or off and no red light when switched on like...